Ablation
All processes by which snow and ice are lost from a glacier, floating ice, or
snow cover.

Acclimatization
The physiological adaptation to climatic variations.

Active Layer
The top layer of soil in permafrost that is subjected to
seasonal freezing and thawing.

Adaptability
See adaptive capacity.

AdaptationAdjustment in natural or human systems in response to actual or expected
climatic stimuli or their effects, which moderates harm or exploits beneficial
opportunities. Various types of adaptation can be distinguished, including anticipatory
and reactive adaptation, private and public adaptation, and autonomous and planned
adaptation:

Anticipatory AdaptationAdaptation that takes place
before impacts of climate change are observed. Also referred to as proactive
adaptation.

Autonomous AdaptationAdaptation that does not constitute
a conscious response to climatic stimuli but is triggered by ecological changes
in natural systems and by market or welfare changes in human systems. Also
referred to as spontaneous adaptation.

Planned AdaptationAdaptation that is the result of a
deliberate policy decision, based on an awareness that conditions have changed
or are about to change and that action is required to return to, maintain,
or achieve a desired state.

Private AdaptationAdaptation that is initiated and implemented
by individuals, households or private companies. Private adaptation is usually
in the actor's rational self-interest.

Public AdaptationAdaptation that is initiated and implemented
by governments at all levels. Public adaptation is usually directed at collective
needs.

Reactive AdaptationAdaptation that takes place after
impacts of climate change have been observed.

Adaptation AssessmentThe practice of identifying options to adapt to climate change and evaluating
them in terms of criteria such as availability, benefits, costs, effectiveness,
efficiency, and feasibility.

Adaptation Benefits
The avoided damage costs or the accrued benefits following the adoption and
implementation of adaptation measures.

Adaptive Capacity
The ability of a system to adjust to climate change (including climate
variability and extremes) to moderate potential damages, to take advantage
of opportunities, or to cope with the consequences.

Aero-AllergensAllergens present in the air.

Aerosols
A collection of airborne solid or liquid particles, with a typical size between
0.01 and 10 mm that reside in the atmosphere for at least several hours. Aerosols
may be of either natural or anthropogenic origin. Aerosols may influence climate
in two ways: directly through scattering and absorbing radiation, and indirectly
through acting as condensation nuclei for cloud formation or modifying the optical
properties and lifetime of clouds.

Afforestation
Planting of new forests on lands that historically have not contained forests.
For a discussion of the term forest and related terms such as afforestation,
reforestation, and deforestation, see the IPCC Special Report on Land
Use, Land-Use Change, and Forestry (IPCC, 2000).

Aggregate Impacts
Total impacts summed up across sectors and/or regions. The aggregation of impacts
requires knowledge of (or assumptions about) the relative importance of impacts
in different sectors and regions. Measures of aggregate impacts include, for
example, the total number of people affected, change in net primary productivity,
number of systems undergoing change, or total economic costs.

Agronomy
The branch of agriculture that deals with the theory and practice of field-crop
production and the scientific management of soil.

Alases
Coalescing thaw depressions.

Albedo
The fraction of solar radiation reflected by a surface or object, often expressed
as a percentage. Snow-covered surfaces have a high albedo; the albedo of soils
ranges from high to low; vegetation-covered surfaces and oceans have a low albedo.
The Earth's albedo varies mainly through varying cloudiness, snow, ice,
leaf area, and land-cover changes.

Algal Blooms
A reproductive explosion of algae in a lake, river, or ocean.

Anadromous Species
A species of fish, such as salmon, that spawn in freshwater then migrate into
the ocean to grow to maturity.

Anaerobic
Living, active, or occurring in the absence of free oxygen.

Anoxia
A deficiency of oxygen, especially of such severity as to result in permanent
damage.

Antarctic Bottomwater
A type of water in the seas surrounding Antarctica with temperatures ranging
from 0 to -0.8°C, salinities from 34.6 to 34.7 PSU, and a density near 27.88.
This is the densest water in the free ocean.

Antarctic Circumpolar Current
A Southern Ocean current that flows around the entire globe driven by the circumpolar
westerlies.

Antarctic Intermediate Water
Created through large-scale cooling and Ekman convergence in the Southern Ocean.

Anthropogenic
Resulting from or produced by human beings.

AOGCM
See climate model.

Apex Consumers
Organisms at the top of food chains; top predators.

Aquaculture
Breeding and rearing fish, shellfish, etc., or growing plants for food in special
ponds.

Aquifer
A stratum of permeable rock that bears water. An unconfined aquifer is recharged
directly by local rainfall, rivers, and lakes, and the rate of recharge will
be influenced by the permeability of the overlying rocks and soils. A confined
aquifer is characterized by an overlying bed that is impermeable and the local
rainfall does not influence the aquifer.

Arbovirus
Any of various viruses transmitted by arthropods and including the causative
agents of dengue fever, yellow fever, and some types of encephalitis.

Arid Regions
Ecosystems with <250 mm precipitation per year.

Autotrophic
Organisms independent of external sources of organic carbon (compounds) for
provision of their own organic constituents, which they can manufacture entirely
from inorganic material. Plants are autotrophic (photoautotrophs) using the
energy of sunlight to produce organic carbon compounds from inorganic carbon
and water in the process of photosynthesis.

Baseflow
Sustained flow in a river or stream that is primarily produced by groundwater
runoff, delayed subsurface runoff, and/or lake outflow.

Baseline/Reference
The baseline (or reference) is any datum against which change is measured. It
might be a "current baseline," in which case it represents observable,
present-day conditions. It might also be a "future baseline," which
is a projected future set of conditions excluding the driving factor of interest.
Alternative interpretations of the reference conditions can give rise to multiple
baselines.

Basin
The drainage area of a stream, river, or lake.

Benthic Organisms
The biota living on, or very near, the bottom of the sea, river, or lake.

Biodiversity
The numbers and relative abundances of different genes (genetic diversity),
species, and ecosystems (communities) in a particular area. See also functional
diversity.

Biofuels
A fuel produced from dry organic matter or combustible oils produced by plants.
Examples of biofuel include alcohol (from fermented sugar), black liquor from
the paper manufacturing process, wood, and soybean oil.

Biomass
The total mass of living organisms in a given area or volume; recently dead
plant material is often included as dead biomass.

Biome
A grouping of similar plant and animal communities into broad landscape units
that occur under similar environmental conditions.

Biosphere
The part of the Earth system comprising all ecosystems and living organisms
in the atmosphere, on land (terrestrial biosphere), or in the oceans (marine
biosphere), including derived dead organic matter, such as litter, soil organic
matter, and oceanic detritus.

Biota
All living organisms of an area; the flora and fauna considered as a unit.

Bog
A poorly drained area rich in accumulated plant material, frequently surrounding
a body of open water and having a characteristic flora (such as sedges, heaths,
and sphagnum).

Boreal Forest
Forests of pine, spruce, fir, and larch stretching from the east coast of Canada
westward to Alaska and continuing from Siberia westward across the entire extent
of Russia to the European Plain.

Breakwater
An offshore structure (such as a wall or jetty) that, by breaking the force
of the wave, protects a harbor, anchorage, beach, or shore area.

C3 Plants
Plants that produce a three-carbon compound during photosynthesis, including
most trees and agricultural crops such as rice, wheat, soybeans, potatoes, and
vegetables.

C4 Plants
Plants that produce a four-carbon compound during photosynthesis (mainly of
tropical origin), including grasses and the agriculturally important crops maize,
sugar cane, millet, and sorghum.

Carbon Cycle
The term used to describe the flow of carbon (in various forms, e.g., as in
carbon dioxide) through the atmosphere, ocean, terrestrial biosphere, and lithosphere.

Carbon Dioxide (CO2)
A naturally occurring gas, also a by-product of burning fossil fuels and biomass,
as well as from land-use changes and other industrial processes. It is the principal
anthropogenic greenhouse gas that affects the Earth's
radiative balance. It is the reference gas against which other greenhouse gases
are measured and therefore has a Global Warming Potential of 1.

Carbon Dioxide Fertilization
The enhancement of the growth of plants as a result of increased atmospheric
carbon dioxide concentration. Depending on their mechanism of photosynthesis,
certain types of plants are more sensitive to changes in atmospheric CO2
concentration. In particular, C3 plants generally show a larger response
to CO2 than C4 plants.

Carbon Flux
Transfer of carbon from one carbon pool to another in units of measurement of
mass per unit area and time (e.g., t C).

Carrying Capacity
The number of individuals in a population that the resources of a habitat
can support.

Catchment
An area that collects and drains rainwater.

Chagas' Disease
A parasitic disease caused by the Trypanosomacruzi and transmitted
by triatomine bugs in the Americas, with two clinical periods: acute (fever,
swelling of the spleen, edemas) and chronic (digestive syndrome, potentially
fatal heart condition).

Climate
Climate in a narrow sense is usually defined as the "average weather,"
or more rigorously, as the statistical description in terms of the mean and
variability of relevant quantities over a period of time ranging from months
to thousands of years. The classical period is 3 decades, as defined by the
World Meteorological Organization (WMO). These quantities are most often surface
variables such as temperature, precipitation, and wind. Climate in a wider sense
is the state, including a statistical description, of the climate system.

Climate Change
Climate change refers to any change in climate over time, whether due to natural
variability or as a result of human activity. This usage differs from that in
the United Nations Framework Convention on Climate Change (UNFCCC), which
defines "climate change" as: "a change of climate which is attributed
directly or indirectly to human activity that alters the composition of the
global atmosphere and which is in addition to natural climate variability observed
over comparable time periods." See also climate variability.

Climate Model (Hierarchy)A numerical representation of the climate system based on the physical,
chemical, and biological properties of its components, their interactions and
feedback processes, and accounting for all or some of its known properties.
The climate system can be represented by models of varying complexity (i.e.,
for any one component or combination of components a hierarchy of models can
be identified, differing in such aspects as the number of spatial dimensions;
the extent to which physical, chemical, or biological processes are explicitly
represented; or the level at which empirical parameterizations are involved.
Coupled atmosphere/ocean/ sea-ice General Circulation Models (AOGCMs) provide
a comprehensive representation of the climate system. There is an evolution
towards more complex models with active chemistry and biology. Climate models
are applied, as a research tool, to study and simulate the climate, but also
for operational purposes, including monthly, seasonal, and interannual climate
predictions.

Climate Prediction
A climate prediction or climate forecast is the result of an attempt to produce
a most likely description or estimate of the actual evolution of the climate
in the future (e.g., at seasonal, interannual, or long-term time scales. See
also climate projection and climate scenario.

Climate ProjectionA projection of the response of the climate system to emission or concentration
scenarios of greenhouse gases and aerosols, or radiative forcing scenarios,
often based upon simulations by climate models. Climate projections are distinguished
from climate predictions in order to emphasize that climate projections
depend upon the emission/concentration/radiative forcing scenario used, which
are based on assumptions, concerning, for example, future socioeconomic andtechnological developments that may or may not be realized and are therefore
subject to substantial uncertainty.

Climate Scenario
A plausible and often simplified representation of the future climate,
based on an internally consistent set of climatological relationships, that
has been constructed for explicit use in investigating the potential consequences
of anthropogenic climate change, often serving as input to impact models. Climate
projections often serve as the raw material for constructing climate scenarios,
but climate scenarios usually require additional information such as about the
observed current climate. A "climate change scenario" is the difference
between a climate scenario and the current climate.

Climate System
The climate system is the highly complex system consisting of five major components:
the atmosphere, the hydrosphere, the cryosphere, the land surface, and
the biosphere, and the interactions between them. The climate system
evolves in time under the influence of its own internal dynamics and because
of external forcings such as volcanic eruptions, solar variations and human-induced
forcings such as the changing composition of the atmosphere and land use.

Climate Variability
Climate variability refers to variations in the mean state and other statistics
(such as standard deviations, the occurrence of extremes, etc.) of the climate
on all temporal and spatial scales beyond that of individual weather events.
Variability may be due to natural internal processes within the climate system
(internal variability), or to variations in natural or anthropogenic external
forcing (external variability). See also climate change.

Coping Range
The variation in climatic stimuli that a system can absorb without producing
significant impacts.

Coral Bleachin
The paling in color of corals resulting from a loss of symbiotic algae. Bleaching
occurs in response to physiological shock in response to abrupt changes in temperature,
salinity, and turbidity.

Cordillera
An individual mountain chain with closely connected, distinct summits. In South
America, "cordillera" refers to an individual mountain range.

Cryosphere
The component of the climate system consisting of all snow, ice, and permafrost
on and beneath the surface of the earth and ocean.

Cryptosporidiosis
An opportunistic infection caused by an intestinal parasite common in animals.
Transmission occurs through ingestion of food or water contaminated with animal
feces. The parasite causes severe chronic diarrhea, especially in people with
HIV.

Deepwater Formation
Occurs when seawater freezes to form sea ice. The local release of salt and
consequent increase in water density leads to the formation of saline coldwater
that sinks to the ocean floor. See Antarctic bottomwater.

Deforestation
Conversion of forest to non-forest. For a discussion of the term forest
and related terms such as afforestation, reforestation, and deforestation,
see the IPCC Special Report on Land Use, Land-Use Change, and Forestry
(IPCC, 2000).

Dengue Fever
An infectious viral disease spread by mosquitoes, often called breakbone fever
because it is characterized by severe pain in joints and back. Subsequent infections
of the virus may lead to dengue haemorrhagic fever (DHF) and dengue shock syndrome
(DSS), which may be fatal.

Desert
An ecosystem with <100 mm precipitation per year.

Desertification
Land degradation in arid, semi-arid, and dry sub-humid areas resulting from
various factors, including climatic variations and human activities. Further,
the United Nations Convention to Combat Desertification (UNCCD) defines land
degradation as a reduction or loss in arid, semi-arid, and dry sub-humid areas
of the biological or economic productivity and complexity of rain-fed cropland,
irrigated cropland, or range, pasture, forest, and woodlands resulting from
land uses or from a process or combination of processes, including those arising
from human activities and habitation patterns, such as: (i) soil erosion caused
by wind and/or water; (ii) deterioration of the physical, chemical, and biological
or economic properties of soil; and (iii) long-term loss of natural vegetation.

Diatom
A class of unicellular algae (Bacillariophyceae) that are widespread on soil
surfaces and in freshwater and marine systems, especially cold waters of relatively
low salinity. These have cell sizes ranging from 5 to 2000 µm.

Disturbance Regime
Frequency, intensity, and types of disturbances, such as fires, inspect or pest
outbreaks, floods, and droughts.

Diurnal Temperature Range
The difference between the maximum and minimum temperature during a day.

Downscaling

Reducing the scale of a model from a global to regional level.

Drought

The phenomenon that exists when precipitation has been significantly below
normal recorded levels, causing serious hydrological imbalances that adversely
affect land resource production systems.

Ecosystem

A distinct system of interacting living organisms, together with their physical
environment. The boundaries of what could be called an ecosystem are somewhat
arbitrary, depending on the focus of interest or study. Thus the extent of an
ecosystem may range from very small spatial scales to, ultimately, the entire
Earth.

Ecosystem Services

Ecological processes or functions which have value to individuals or society.

Ecotone

Transition area between adjacent ecological communities (e.g., between forests
and grasslands), usually involving competition between organisms common to both.

Edaphic
Of or relating to the soil; factors inherent in the soil.

Effective Rainfall

The portion of the total rainfall that becomes available for plant growth.

El Niño-Southern Oscillation (ENSO)

El Niño, in its original sense, is a warmwater current that periodically
flows along the coast of Ecuador and Peru, disrupting the local fishery. This
oceanic event is associated with a fluctuation of the intertropical surface
pressure pattern and circulation in the Indian and Pacific Oceans, called the
Southern Oscillation. This coupled atmosphere-ocean phenomenon is collectively
known as El Niño-Southern Oscillation. During an El Niño event,
the prevailing trade winds weaken and the equatorial countercurrent strengthens,
causing warm surface waters in the Indonesian area to flow eastward to overlie
the cold waters of the Peru current. This event has great impact on the wind,
sea surface temperature, and precipitation patterns in the tropical Pacific.
It has climatic effects throughout the Pacific region and in many other parts
of the world. The opposite of an El Niño event is called La Niña.

Emission Scenario
A plausible representation of the future development of emissions of substances
that are potentially radiatively active (e.g., greenhouse gases, aerosols),
based on a coherent and internally consistent set of assumptions about driving
forces (such as demographic and socioeconomic development, technological change)
and their key relationships. In 1992, the IPCC presented a set of emission scenarios
that were used as a basis for the climate projections in the Second Assessment
Report (IPCC, 1996). These emission scenarios are referred to as the IS92 scenarios.
In the IPCC Special Report on Emission Scenarios (Nakicenovic et al.,
2000), new emission scenarios--the so-called SRES scenarios--were published.

Endemic
Restricted or peculiar to a locality or region. With regard to human health,
endemic can refer to a disease or agent present or usually prevalent in a population
or geographical area at all times.

Endorheic Lake
A lake with no outflow; also known as a closed lake.

Enzootic
A disease affecting the animals in an area. It corresponds to an endemic
disease among humans.

Epidemic
Occurring suddenly in numbers clearly in excess of normal expectancy, said especially
of infectious diseases but applied also to any disease, injury, or other health-related
event occurring in such outbreaks.

Erosion
The process of removal and transport of soil and rock by weathering, mass wasting,
and the action of streams, glaciers, waves, winds, and underground water.

Eustatic Sea-Level Rise

See sea-level rise.

Eutrophication
The process by which a body of water (often shallow) becomes (either naturally
or by pollution) rich in dissolved nutrients with a seasonal deficiency in dissolved
oxygen.

Evaporation
The process by which a liquid becomes a gas.

Evapotranspiration
The combined process of evaporation from the Earth's surface and transpiration
from vegetation.

Exoheic Lake
A lake drained by outflowing rivers.

Exotic Species
See introduced species.

ExposureThe nature and degree to which a system is exposed to significant climatic
variations.

Exposure UnitAn activity, group, region, or resource that is subjected to climatic stimuli.

Externalities
By-products of activities that affect the well-being of people or the environment,
where those impacts are not reflected in market prices. The costs (or benefits)
associated with externalities do not enter cost-accounting schemes.

ExtinctionThe complete disappearance of an entire species.

ExtirpationThe disappearance of a species from part of its range; local extinction.

Extreme Weather EventAn event that is rare within its statistical reference distribution at a
particular place. Definitions of "rare" vary, but an extreme weather event would
normally be as rare as or rarer than the 10th or 90th percentile. By definition,
the characteristics of what is called "extreme weather" may vary from place
to place. An "extreme climate event" is an average of a number of weather events
over a certain period of time, an average which is itself extreme (e.g., rainfall
over a season).

Extrinsic Incubation PeriodIn blood-feeding anthropod vectors, the time between acquisition of the
infectious blood meal and the time when the anthropod becomes capable of transmitting
the agent. In the case of malaria, the life stages of the plasmodium parasite
spent within the female mosquito vector (i.e., outside the human host).

Feedback A process that triggers changes in a second process that in turn influences
the original one; a positive feedback intensifies the original process, and
a negative feedback reduces it.

Fen

Low land covered wholly or partly with water unless artificially drained.

Fiber

Wood, fuelwood (either woody or non-woody).

Food Insecurity

A situation that exists when people lack secure access to sufficient amounts
of safe and nutritious food for normal growth and development and an active
and healthy life. It may be caused by the unavailability of food, insufficient
purchasing power, inappropriate distribution, or inadequate use of food at the
household level. Food insecurity may be chronic, seasonal, or transitory.

Forecast

See climate prediction and climate projection.

Forest

A vegetation type dominated by trees. Many definitions of the term forest
are in use throughout the world, reflecting wide differences in biogeophysical
conditions, social structure, and economics. For a discussion of the term forest
and related terms such as afforestation, reforestation, and deforestation,
see the IPCC Special Report on Land Use, Land-Use Change, and Forestry
(IPCC, 2000).

Freshwater Lens

A lenticular fresh groundwater body that underlies an oceanic island. It is
underlain by saline water.

Functional Diversity

The number of functionally different organisms in an ecosystem (also referred
to as "functional types" and "functional groups").

General Circulation Model (GCM)

See climate model.

General Equilibrium Analysis

An approach that considers simultaneously all the markets in an economy, allowing
for feedback effects between individual markets.

Geomorphic

Pertaining to the form of the Earth or its surface features.

Glacier
A mass of land ice flowing downhill (by internal deformation and sliding at
the base) and constrained by the surrounding topography (e.g., the sides of
a valley or surrounding peaks); the bedrock topography is the major influence
on the dynamics and surface slope of a glacier. A glacier is maintained by accumulation
of snow at high altitudes, balanced by melting at low altitudes or discharge
into the sea.

Greenhouse Effect

Greenhouse gases effectively absorb infrared radiation emitted by the Earth's
surface, by the atmosphere itself due to the same gases, and by clouds. Atmospheric
radiation is emitted to all sides, including downward to the Earth's surface.
Thus greenhouse gases trap heat within the surface-troposphere system. This
is called the "natural greenhouse effect." Atmospheric radiation is strongly
coupled to the temperature of the level at which it is emitted. In the troposphere,
the temperature generally decreases with height. Effectively, infrared radiation
emitted to space originates from an altitude with a temperature of on average
-19°C, in balance with the net incoming solar radiation, whereas the Earth's
surface is kept at a much higher temperature of on average 14°C. An increase
in the concentration of greenhouse gases leads to an increased infrared opacity
of the atmosphere, and therefore to an effective radiation into space from a
higher altitude at a lower temperature. This causes a radiative forcing, an
imbalance that can only be compensated for by an increase of the temperature
of the surface-troposphere system. This is called the "enhanced greenhouse effect."

Greenhouse Gas

Greenhouse gases are those gaseous constituents of the atmosphere, both natural
and anthropogenic, that absorb and emit radiation at specific wavelengths within
the spectrum of infrared radiation emitted by the Earth's surface, the atmosphere,
and clouds. This property causes the greenhouse effect. Water vapor (H2O),
carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4),
and ozone (O3) are the primary greenhouse gases in the Earth's atmosphere.
Moreover, there are a number of entirely human-made greenhouse gases in the
atmosphere, such as the halocarbons and other chlorine- and bromine-containing
substances which are dealt with under the Montreal Protocol. Beside CO2,
N2O, and CH4, the Kyoto Protocol deals with the
greenhouse gases sulfur hexaflouride (SF6), hydrofluorocarbons (HFCs)
and perfluorocarbons (PFCs).

Groin

A low, narrow jetty, usually extending roughly perpendicular to the shoreline,
designed to protect the shore from erosion by currents, tides, or waves, or
to trap sand for the purpose of building up or making a beach.

Gross Primary Production

The amount of carbon fixed from the atmosphere through photosynthesis.

Groundwater Recharge

The process by which external water is added to the zone of saturation of
an aquifer, either directly into a formation or indirectly by way of
another formation.

Habitat

The particular environment or place where an organism or species tends to
live; a more locally circumscribed portion of the total environment.

Halocline

A layer in the ocean in which the rate of salinity variation with depth is
much larger than layers immediately above or below it.

Hantavirus

A virus in the family Bunyaviridae that causes a type of haemorrhagic fever.
It is thought that humans catch the disease mainly from infected rodents, either
through direct contact with the animals or by inhaling or ingesting dust that
contains their dried urine.

Heath

Any of the various low-growing shrubby plants of open wastelands, usually
growing on acidic, poorly drained soils.

Heat Island

An area within an urban area characterized by ambient temperatures higher than
those of the surrounding area because of the absorption of solar energy by materials
like asphalt.

Herbaceous

Flowering, non-woody plants.

Heterotrophic Respiration

The release of CO2 from decomposition of organic matter.

Highland Malaria

Malaria that occurs around the altitudinal limits of its distribution.

Human Settlement

A place or area occupied by settlers.

Human System

Any system in which human organizations play a major role. Often, but not
always, the term is synonymous with "society" or "social system" (e.g., agricultural
system, political system, technological system, economic system); all are human
systems in the sense applied in the TAR.

Hypolimnion

The part of a lake below the thermocline made up of water that is stagnant
and of essentially uniform temperature except during the period of overturn.

Ice Cap

A dome-shaped ice mass covering a highland area that is considerably smaller
in extent than ice sheets.

Ice Jam

An accumulation of broken river or sea ice caught in a narrow channel.

Ice Sheet

A mass of land ice which is sufficiently deep to cover most of the underlying
bedrock topography, so that its shape is mainly determined by its internal dynamics
(the flow of the ice as it deforms internally and slides at its base). An ice
sheet flows outwards from a high central plateau with a small average surface
slope. The margins slope steeply, and the ice is discharged through fast-flowing
ice streams or outlet glaciers, in some cases into the sea or into ice shelves
floating on the sea. There are only two large ice sheets in the modern world--on
Greenland and Antarctica, the Antarctic ice sheet being divided into east and
west by the Transantarctic Mountains; during glacial periods there were others.

Ice Shelf

A floating ice sheet of considerable thickness attached to a coast
(usually of great horizontal extent with a level or gently undulating surface);
often a seaward extension of ice sheets.

Immunosuppression

Reduced functioning of an individual's immune system.

(Climate) Impact Assessment

The practice of identifying and evaluating the detrimental and beneficial
consequences of climate change on natural and human systems.

(Climate) Impacts

Consequences of climate change on natural and human systems. Depending on the
consideration of adaptation, one can distinguish between potential impacts and
residual impacts.

Potential Impacts--All impacts that may occur given a projected
change in climate, without considering adaptation.

Residual Impacts--The impacts of climate change that would
occur after adaptation.

See also aggregate impacts, market impacts, and non-market
impacts.

Indigenous Peoples

People whose ancestors inhabited a place or a country when persons from another
culture or ethnic background arrived on the scene and dominated them through
conquest, settlement, or other means and who today live more in conformity with
their own social, economic, and cultural customs and traditions than those of
the country of which they now form a part (also referred to as "native," "aboriginal,"
or "tribal" peoples)

Industrial Revolution

A period of rapid industrial growth with far-reaching social and economic
consequences, beginning in England during the second half of the 18th century
and spreading to Europe and later to other countries including the United States.
The industrial revolution marks the beginning of a strong increase in the use
of fossil fuels and emission of in particular fossil carbon dioxide. In the
TAR, the terms "pre-industrial" and "industrial" refer, somewhat arbitrarily,
to the periods before and after 1750, respectively.

Infectious Diseases

Any disease that can be transmitted from one person to another. This may occur
by direct physical contact, by common handling of an object that has picked
up infective organisms, through a disease carrier, or by spread of infected
droplets coughed or exhaled into the air.

Infrastructure

The basic equipment, utilities, productive enterprises, installations, and
services essential for the development, operation, and growth of an organization,
city, or nation.

Insolvency

Inability to meet financial obligations; bankruptcy.

Integrated Assessment

A method of analysis that combines results and models from the physical, biological,
economic, and social sciences, and the interactions between these components,
in a consistent framework to evaluate the status and the consequences of environmental
change and the policy responses to it.

Introduced Species

A species occurring in an area outside its historically known natural range
as a result of accidental dispersal by humans (also referred to as "exotic species"
or "alien species").

Invasive Species

An introduced species that invades natural habitats.

Keystone Species

A species that has a central servicing role affecting many other organisms
and whose demise is likely to result in the loss of a number of species and
lead to major changes in ecosystem function.

Kyoto Protocol
The Kyoto Protocol was adopted at the Third Session of the Conference of the
Parties (COP) to the UN Framework Convention on Climate Change (UNFCCC)
in 1997 in Kyoto, Japan. It contains legally binding commitments, in addition
to those included in the UNFCCC. Countries included in Annex B of the Protocol
(most OECD countries and EITs) agreed to reduce their anthropogenic GHG emissions
(CO2, CH4, N2O, HFCs, PFCs, and SF6)
by at least 5% below 1990 levels in the commitment period 2008 to 2012. The
Kyoto Protocol has not yet entered into force (as of June 2001).

La Niña

See El Niño-Southern Oscillation (ENSO).

Land Use

The total of arrangements, activities, and inputs undertaken in a certain
land-cover type (a set of human actions). The social and economic purposes for
which land is managed (e.g., grazing, timber extraction, conservation).

Landslide
A mass of material that has slipped downhill by gravity, often assisted by water
when the material is saturated; rapid movement of a mass of soil, rock, or debris
down a slope.

Large-Scale Singularities

Abrupt and dramatic changes in systems in response to smooth changes in driving
forces. For example, a gradual increase in atmospheric greenhouse gas concentrations
may lead to such large-scale singularities as slowdown or collapse of the thermohaline
circulation or collapse of the West Antarctic Ice Sheet. The occurrence, magnitude,
and timing of large-scale singularities are difficult to predict.

Leaching

The removal of soil elements or applied chemicals through percolation.

Legume

Plants that are able to fix nitrogen from the air through a symbiotic relationship
with soil bacteria (e.g., peas, beans, alfalfa, clovers).

Limnology

Study of lakes and their biota.

Littoral Zone

A coastal region; the shore zone between high and low watermarks.

Local Agenda 21
Local Agenda 21s are the local plans for environment and development that each
local authority is meant to develop through a consultative process with their
populations, with particular attention paid to involving women and youth. Many
local authorities have developed Local Agenda 21s through consultative processes
as a means of reorienting their policies, plans, and operations towards the
achievement of sustainable development goals. The term comes from Chapter
28 of Agenda 21--the document formally endorsed by all government representatives
attending the UN Conference on Environment and Development (also known as the
Earth Summit) in Rio de Janeiro in 1992.

Maladaptation

Any changes in natural or human systems that inadvertently increase vulnerability
to climatic stimuli; an adaptation that does not succeed in reducing vulnerability
but increases it instead.

Malaria

Endemic or epidemic parasitic disease caused by species of the genus Plasmodium
(protozoa) and transmitted by mosquitoes of the genus Anopheles; produces high
fever attacks and systemic disorders, and kills approximately 2 million people
every year.

Market Impacts

Impacts that are linked to market transactions and directly affect
gross domestic product (GDP, a country's national accounts)--for example, changes
in the supply and price of agricultural goods. See also non-market impacts.

Mass Movement

Applies to all unit movements of land material propelled and controlled by
gravity.

Meningitis

Inflammation of the meninges (part of the covering of the brain).

Metazoan

An animal whose body consists of many cells. See also protozoan

Microbial Loop

Complex food web involving bacteria, single-celled animals and plants, viruses,
and dissolved and particulate organic material. Dissolved and particulate material,
released from organisms, is utilized by bacteria, which are grazed by protozoa
which in turn are grazed by metazoa. Around 50% (often more) of primary production
passes through the microbial loop rather than along the classical food chain
of phyto plankton to herbivore.

Microclimate

Local climate at or near the Earth's surface. See also climate.

Mitigation

An anthropogenic intervention to reduce the sources or enhance the
sinks of greenhouse gases.

Mixed Layer

The upper region of the ocean well-mixed by interaction with the overlying
atmosphere.

Monsoon

Wind in the general atmospheric circulation typified by a seasonal persistent
wind direction and by a pronounced change in direction from one season to the
next.

Montane

The biogeographic zone made up of relatively moist, cool upland slopes below
timberline and characterized by the presence of large evergreen trees as a dominant
lifeform.

Montreal Protocol

The Montreal Protocol on Substances that Deplete the Ozone Layer was adopted
in Montreal in 1987, and subsequently adjusted and amended in London (1990),
Copenhagen (1992), Vienna (1995), Montreal (1997), and Beijing (1999). It controls
the consumption and production of chlorine- and bromine-containing chemicals
that destroy stratospheric ozone, such as CFCs, methyl chloroform, carbon
tetrachloride, and many others.

Morbidity

Rate of occurrence of disease or other health disorder within a population,
taking account of the age-specific morbidity rates. Health outcomes include
chronic disease incidence/ prevalence, rates of hospitalization, primary care
consultations, disability-days (i.e., days when absent from work), and prevalence
of symptoms.

Morphology

The form and structure of an organism or any of its parts.

Mortality

Rate of occurrence of death within a population within a specified time period;
calculation of mortality takes account of age-specific death rates, and can
thus yield measures of life expectancy and the extent of premature death.

NanoplanktonPhytoplankton whose lengths range from 10-50 µm.

Net Biome Production (NBP)
Net gain or loss of carbon from a region. NBP is equal to Net Ecosystem Production
minus the carbon lost due to a disturbance (e.g., a forest fire or a forest
harvest).

Net Ecosystem Production (NEP)

Net gain or loss of carbon from an ecosystem. NEP is equal to Net Primary
Production minus the carbon lost through heterotrophic respiration.

Net Primary Production (NPP)

The increase in plant biomass or carbon of a unit of a landscape. NPP is equal
to Gross Primary Production minus carbon lost through autotrophic respiration.

Nitrogen Oxides (NOx)

Any of several oxides of nitrogen.

Non-Linearity

A process is called "non-linear" when there is no simple proportional relation
between cause and effect.

Non-Market Impacts

Impacts that affect ecosystems or human welfare, but that are not directly
linked to market transactions--for example, an increased risk of premature death.
See also market impacts.

Non-Point-Source Pollution

Pollution from sources that cannot be defined as discrete points, such as
areas of crop production, timber, surface mining, disposal of refuse, and construction.
See also point-source pollution.

No Regrets Policy

One that would generate net social benefits whether or not there is anthropogenic
climate change.

North Atlantic Oscillation (NAO)

The North Atlantic Oscillation consists of opposing variations of barometric
pressure near Iceland and near the Azores. It is the dominant mode of winter
climate variability in the North Atlantic region ranging from central North
America to Europe.

Obligate Species

Species restricted to one particularly characteristic mode of life.

Ocean Conveyor Belt

The theoretical route by which water circulates around the entire global ocean,
driven by wind and the thermohaline circulation.

Ocean Ventilation
Downwelling of water from near the surface to the deep ocean. See also deepwater
formation.

Oligotrophic

Relatively unproductive areas of the sea, lakes, and rivers with low nutrient
content. See also eutrophic.

Opportunity Costs

The cost of an economic activity forgone by the choice of another activity.

Orography

The study of the physical geography of mountains and mountain systems.

Ozone

Ozone, the triatomic form of oxygen (O3), is a gaseous atmospheric
constituent. In the troposphere, it is created both naturally and by photochemical
reactions involving gases resulting from human activities (photochemical
smog). In high concentrations, tropospheric ozone can be harmful to a wide-range
of living organisms. Tropospheric ozone acts as a greenhouse gas. In
the stratosphere, ozone is created by the interaction between solar ultraviolet
radiation and molecular oxygen (O2). Stratospheric ozone plays a
decisive role in the stratospheric radiative balance. Depletion of stratospheric
ozone, due to chemical reactions that may be enhanced by climate change,
results in an increased ground-level flux of ultraviolet (UV-) B radiation.
See also Montreal Protocol.

Particulates

Very small solid exhaust particles emitted during the combustion of fossil
and biomass fuels. Particulates may consist of a wide variety of substances.
Of greatest concern for health are particulates of less than or equal to 10
nm in diameter, usually designated as PM10.

Perennially frozen ground that occurs wherever the temperature remains below
0°C for several years.

Phenology
The study of natural phenomena that recur periodically (e.g., blooming, migrating)
and their relation to climate and seasonal changes.

Photic Zone

The upper waters of lakes, rivers, and sea sufficiently illuminated for photosynthesis
to occur.

Photochemical Smog

A mix of photochemical oxidant air pollutants produced by the reaction of sunlight
with primary air pollutants, especially hydrocarbons.

Photosynthate
The product of photosynthesis.

Photosynthesis

The process by which plants take carbon dioxide from the air (or bicarbonate
in water) to build carbohydrates, releasing oxygen in the process. There are
several pathways of photosynthesis with different responses to atmospheric CO2
concentrations. See also CO2 fertilization,
C3 plants, and C4 plants.

Physiographic

Of, relating to, or employing a description of nature or natural phenomena.

Phytophagous Insects

Insects that feed on plants.

Phytoplankton

The plant forms of plankton (e.g., diatoms). Phytoplankton are
the dominant plants in the sea, and are the bast of the entire marine food web.
These single-celled organisms are the principal agents for photosynthetic carbon
fixation in the ocean. See also zooplankton.

Plankton

Aquatic organisms that drift or swim weakly. See also phytoplankton and
zooplankton.

Point-Source Pollution

Pollution resulting from any confined, discrete source, such as a pipe, ditch,
tunnel, well, container, concentrated animal-feeding operation, or floating
craft. See also non-point-source pollution.

Polynyas

Areas of open water in pack ice or sea ice.

Pool

See reservoir.

Potential Production

Estimated production of a crop under conditions when nutrients and water are
available at optimum levels for plant growth and development; other conditions
such as day length, temperature, soil characteristics, etc., determined by site
characteristics.

Pre-Industrial

See Industrial Revolution.

Primary Energy

Energy embodied in natural resources (e.g., coal, crude oil, sunlight, uranium)
that has not undergone any anthropogenic conversion or transformation.

Producer Surplus

Returns beyond the cost of production that provide compensation for owners
of skills or assets that are scarce (e.g., agriculturally productive land).

Projection (Generic)

A projection is a potential future evolution of a quality or set of quantities,
often computed with the aid of a model. Projections are distinguished from predictions
in order to emphasize that projections involve assumptions--concerning, for
example, future socioeconomic and technological developments that may or may
not be realized--and are therefore subject to substantial uncertainty. See also
climate projection and climate prediction.

Protozoan

A single-celled animal.

Radiative Forcing

Radiative forcing is the change in the net vertical irradiance [expressed
in Watts per square meter (Wm-2)] at the tropopause due to an internal
change or a change in the external forcing of the climate system, such as a
change in the concentration of CO2 or the output of the Sun. Usually
radiative forcing is computed after allowing for stratospheric temperatures
to readjust to radiative equilibrium, but with all tropospheric properties held
fixed at their unperturbed values.

Rangeland
Unimproved grasslands, shrublands, savannas, and tundra.

Reference Scenario
See baseline/reference.

Reforestation

Planting of forests on lands that have previously contained forests
but that have been converted to some other use. For a discussion of the term
forest and related terms such as afforestation, reforestation,
and deforestation, see the IPCC Special Report on Land Use, Land-Use
Change, and Forestry (IPCC, 2000).

Regeneration

The renewal of a stand of trees through either natural means (seeded onsite
or adjacent stands or deposited by wind, birds, or animals) or artificial means
(by planting seedlings or direct seeding).

Reinsurance

The transfer of a portion of primary insurance risks to a secondary tier of
insurers (reinsurers); essentially "insurance for insurers."

Reservoir

A component of the climate system, other than the atmosphere, that has the
capacity to store, accumulate, or release a substance of concern (e.g., carbon,
a greenhouse gas, or precursor). Oceans, soils, and forests are
examples of reservoirs of carbon. "Pool" is an equivalent term (note that the
definition of pool often includes the atmosphere). The absolute quantity of
substances of concern held within a reservoir at a specified time is called
the "stock." The term also means an artificial or natural storage place for
water, such as a lake, pond, or aquifer, from which the water may be
withdrawn for such purposes as irrigation, water supply, or irrigation.

Reservoir HostAny animal, plant, soil, or inanimate matter in which a pathogen normally
lives and multiplies, and on which it depends primarily for survival (e.g.,
foxes are a reservoir for rabies). Reservoir hosts may be asymptomatic.

Riparian
Relating to or living or located on the bank of a natural watercourse (as a
river) or sometimes of a lake or a tidewater.

Runoff

That part of precipitation that does not evaporate. In some countries, runoff
implies surface runoff only.

Salinization
The accumulation of salts in soils.

Saltwater Intrusion/Encroachment

Displacement of fresh surface water or groundwater by the advance of saltwater
due to its greater density, usually in coastal and estuarine areas.

Scenario (Generic)

A plausible and often simplified description of how the future may develop,
based on a coherent and internally consistent set of assumptions about driving
forces and key relationships. Scenarios may be derived from projections, but
are often based on additional information from other sources, sometimes combined
with a "narrative storyline." See also climate scenario and emissions
scenario.

Sea-Level Rise

An increase in the mean level of the ocean. Eustatic sea-level rise is a change
in global average sea level brought about by an alteration to the volume of
the world ocean. Relative sea-level rise occurs where there is a net increase
in the level of the ocean relative to local land movements. Climate modelers
largely concentrate on estimating eustatic sea-level change. Impact researchers
focus on relative sea-level change.

Seawall
A human-made wall or embankment along a shore to prevent wave erosion.

Semi-Arid Regions

Ecosystems that have >250 mm precipitation per year, but are not highly
productive; usually classified as rangelands.

Sensitivity

Sensitivity is the degree to which a system is affected, either adversely
or beneficially, by climate-related stimuli. The effect may be direct
(e.g., a change in crop yield in response to a change in the mean, range, or
variability of temperature) or indirect (e.g., damages caused by an increase
in the frequency of coastal flooding due to sea level rise).

Sequestration

The process of increasing the carbon content of a carbon pool other than the
atmosphere.

Silt

Unconsolidated or loose sedimentary material whose constituent rock particles
are finer than grains of sand and larger than clay particles.

Silviculture

Development and care of forests.

Sink

Any process, activity, or mechanism that removes a greenhouse gas,
an aerosol, or a precursor of a greenhouse gas or aerosol from the atmosphere.

Snowpacks

A seasonal accumulation of slow-melting snow.

Soil Carbon Pool

Refers to the relevant carbon in the soil. It includes various forms of soil
organic carbon (humus) and inorganic soil carbon and charcoat. It excludes soil
biomass (e.g., roots, bulbs, etc.) as well as the soil fauna (animals).

Source

Any process, activity, or mechanism that releases a greenhouse gas,
an aerosol, or a precursor of a greenhouse gas or aerosol into the atmosphere.

Southern Oscillation

A large-scale atmospheric and hydrospheric fluctuation centered in the equatorial
Pacific Ocean, exhibiting a pressure anomaly, alternatively high over the Indian
Ocean and high over the South Pacific. Its period is slightly variable, averaging
2.33 years. The variation in pressure is accompanied by variations in wind strengths,
ocean currents, sea-surface temperatures, and precipitation in the surrounding
areas.

Stakeholders

Person or entity holding grants, concessions, or any other type of value that
would be affected by a particular action or policy.

Stimuli (Climate-Related)

All the elements of climate change, including mean climate characteristics,
climate variability, and the frequency and magnitude of extremes.

Stochastic Events

Events involving a random variable, chance, or probability.

Stock

See reservoir.

Stratosphere

Highly stratified region of atmosphere above the troposphere extending
from about 10 km (ranging from 9 km in high latitudes to 16 km in the tropics
on average) to about 50 km.

Streamflow

Water within a river channel, usually expressed in m3 sec-1.

Sub-Antarctic Mode Water (SAMW)
A type of water in the Sub-Antarctic Zone of the Southern Ocean. The SAMW is
the deep surface layer of water with uniform temperature and salinity created
by convective processes in the winter. It can be identified by a temperature
of around -1.8°C and a salinity of around 34.4 PSU, and is separated from
the overlying surface water by a halocline at around 50 m in the summer. Although
it is not considered to be a water mass, it contributes to the Central Water
of the Southern Hemisphere, and is additionally responsible for the formation
of Antarctic Intermediate Water in the eastern part of the South Pacific Ocean.
It is also known as Winter Water.

Submergence
A rise in the water level in relation to the land, so that areas of formerly
dry land become inundated; it results either from a sinking of the land or from
a rise of the water level.

Subsidence

The sudden sinking or gradual downward settling of the Earth's surface with
little or no horizontal motion.

Succession

Transition in the composition of plant communities following disturbance.

Surface Runoff

The water that travels over the soil surface to the nearest surface stream;
runoff of a drainage basin that has not passed beneath the surface since
precipitation.

Sustainable Development

Development that meets the needs of the present without compromising the ability
of future generations to meet their own needs.

Synoptic
Relating to or displaying atmospheric and weather conditions as they exist simultaneously
over a broad area.

Taiga

Coniferous forests of northern North America and Eurasia.

Thermal Erosion

The erosion of ice-rich permafrost by the combined thermal and mechanical
action of moving water.

Thermal Expansion

In connection with sea-level rise, this refers to the increase in volume
(and decrease in density) that results from warming water. A warming of the
ocean leads to an expansion of the ocean volume and hence an increase in sea
level.

Thermocline

The region in the world's ocean, typically at a depth of 1 km, where temperature
decreases rapidly with depth and which marks the boundary between the surface
and the ocean.

Thermohaline Circulation

Large-scale density-driven circulation in the ocean, caused by differences
in temperature and salinity. In the North Atlantic, the thermohaline circulation
consists of warm surface water flowing northward and cold deepwater flowing
southward, resulting in a net poleward transport of heat. The surface water
sinks in highly restricted sinking regions located in high latitudes.

Timberline
The upper limit of tree growth in mountains or high latitudes.

Transpiration

The emission of water vapor from the surfaces of leaves or other plant parts.

Troposphere

The lowest part of the atmosphere from the surface to about 10 km in altitude
in mid-latitudes (ranging from 9 km in high latitudes to 16 km in the tropics
on average) where clouds and "weather" phenomena occur. In the troposphere,
temperatures generally decrease with height.

Tsunami

A large tidal wave produced by a submarine earthquake, landslide, or volcanic
eruption.

Tundra

A treeless, level, or gently undulating plain characteristic of arctic and
subarctic regions.

Ultraviolet (UV)-B Radiation

Solar radiation within a wavelength range of 280-320 nm, the greater part
of which is absorbed by stratospheric ozone. Enhanced UV-B radiation
suppresses the immune system and can have other adverse effects on living organisms.

Uncertainty
An expression of the degree to which a value (e.g., the future state of the
climate system) is unknown. Uncertainty can result from lack of information
or from disagreement about what is known or even knowable. It may have many
types of sources, from quantifiable errors in the data to ambiguously defined
concepts or terminology, or uncertain projections of human behavior. Uncertainty
can therefore be represented by quantitative measures (e.g., a range of values
calculated by various models) or by qualitative statements (e.g., reflecting
the judgment of a team of experts).

Undernutrition

The result of food intake that is insufficient to meet dietary energy requirements
continuously, poor absorption, and/or poor biological use of nutrients consumed.

Unique and Threatened Systems
Entities that are confined to a relatively narrow geographical range but can
affect other, often larger entities beyond their range; narrow geographical
range points to sensitivity to environmental variables, including climate, and
therefore attests to potential vulnerability to climate change.

United Nations Framework Conventionon Climate Change (UNFCCC)

The Convention was adopted on 9 May 1992, in New York, and signed at the 1992
Earth Summit in Rio de Janeiro by more than 150 countries and the European Community.
Its ultimate objective is the "stabilization of greenhouse gas concentrations
in the atmosphere at a level that would prevent dangerous anthropogenic interference
with the climate system." It contains commitments for all Parties. Under the
Convention, Parties included in Annex I aim to return greenhouse gas emissions
not controlled by the Montreal Protocol to 1990 levels by the year 2000. The
Convention entered in force in March 1994. See also Kyoto Protocol.

Transport of deeper water to the surface, usually caused by horizontal movements
of surface water.

Urbanization

The conversion of land from a natural state or managed natural state (such
as agriculture) to cities; a process driven by net rural-to-urban migration
through which an increasing percentage of the population in any nation or region
come to live in settlements that are defined as "urban centers."

Vector

An organism, such as an insect, that transmits a pathogen from one host to
another. See also vector-borne diseases and vectorial capacity.

Vector-Borne Diseases

Disease that is transmitted between hosts by a vector organism (such
as a mosquito or tick-- for example, malaria, dengue fever, and leishmaniasis.

Vectorial Capacity

Quantitative term used in the study of the transmission dynamics of malaria
to express the average number of potentially infective bites of all vectors
feeding upon one host in one day, or the number of new inoculations with a vector-borne
disease transmitted by one vector species from one infective host in one day.

Vernalization

The act or process of hastening the flowering and fruiting of plants by treating
seeds, bulbs, or seedlings so as to induce a shortening of the vegetative period.

Vulnerability

The degree to which a system is susceptible to, or unable to cope with, adverse
effects of climate change, including climate variability and extremes. Vulnerability
is a function of the character, magnitude, and rate of climate variation to
which a system is exposed, its sensitivity, and its adaptive capacity.

Water Consumption

Amount of extracted water irretrievably lost at a given territory during it's
use (evaporation and goods production). Water consumption is equal to water
withdrawal minus return flow.

Water Stress
A country is water stressed if the available freshwater supply relative to water
withdrawals acts as an important constraint on development. Withdrawals
exceeding 20% of renewable water supply has been used as an indicator of water
stress.

Water Withdrawal
Amount of water extracted from water bodies.

Water Use Efficiency

Carbon gain in photosynthesis per unit water lost in evapotranspiration. It
can be expressed on a short-term basis as the ratio of photosynthetic carbon
gain per unit transpirational water loss, or on a seasonal basis as the ratio
of net primary production or agricultural yield to the amount of available
water.

Xeric
Requiring only a small amount of moisture.

Zoonosis

The transmission of a disease from an animal or nonhuman species to humans.
The natural reservoir is a nonhuman animal.

Zooplankton

The animal forms of plankton. They consume phytoplankton or
other zooplankton. See also phytoplankton.